1. Field of the Invention
The present invention relates to the drive circuit of a plasma display panel, and more particularly to the drive circuit of a plasma display panel that can limit the concentration of elements that generate heat during charge recovery.
2. Description of the Related Art
Generally, plasma display panels offer the advantages of thin structure, freedom from flicker, a high display contrast ratio, the relative ease of production in a large-screen format, rapid response speed, and the capability for multicolor light emission through the use of phosphors in spontaneous light emission forms. The use of plasma display panels is consequently becoming more widespread in recent years in the fields of large public display devices and in color television.
As shown in FIG. 1, an example of the prior art is constituted by panel 608 for display light emission and a drive circuit for controlling the display content and display luminance of panel 608.
Panel 608 is made up of pairs of main electrodes composed of scan electrodes 606-1˜606-n and sustain electrodes 605-1˜606-n that are arranged parallel to each other and data electrodes 607-1˜607-N that extend perpendicular to these main electrodes. The main electrodes and data electrodes 607-1˜607-N intersect in a matrix, each one of these intersecting portions forming a picture element.
In addition, the drive circuit of panel 608 is made up by: scan driver circuit 602 for driving scan electrodes 606-1˜606-n; data driver circuit 604 for driving data electrodes 607-1˜607-N; sustain driver circuit 601 for sustaining the emission of panel 608; and control circuit 603 for controlling scan driver circuit 602, data driver circuit 604, and sustain driver circuit 601. Control circuit 603 is made up by: scan driver control unit 609 for controlling scan driver circuit 602, data driver control unit 610 for controlling data driver circuit 604, and sustain driver control unit 611 for controlling sustain driver circuit 601.
In a plasma display panel that is configured according to the foregoing description, a display portion in panel 608 is first selected by scan electrodes 606-1˜606-n and data electrodes 607-1˜607-N (write discharge interval). Voltage is then alternately applied between scan electrodes 606-1˜606-n and sustain electrodes 605-1˜605-n, and the desired display is realized by the resulting discharge (sustain discharge interval). The luminance of the display is determined by the number of repetitions of the alternate application of voltage between scan electrodes 606-1˜606-n and sustain electrodes 605-1˜605-n. 
The method of sustaining discharge by the exchange of charge between scan electrodes 606-1˜606-n and sustain electrodes 605-1˜605-n in this way is referred to as the self-recovery method. In this self-recovery method, charge that is generated in the write discharge interval is also used in the sustaining discharge, and new charge therefore need not be generated when generating the sustaining discharge. This method therefore has the advantage of enabling a reduction in power consumption.
As shown in FIG. 2, sustain driver circuit 601 shown in FIG. 1 is made up by: transistor Q702 for clamping sustain electrodes 605-1˜605-n to the potential of power-supply voltage VS; transistor Q703 for clamping sustain electrodes 605-1˜605-n to the ground potential; transistor Q706 for clamping scan electrodes 606-1˜606-n˜to the potential of the power-supply voltage VS; transistor Q707 for clamping scan electrodes˜606-1˜606-n to the ground potential; transistors Q704, Q705, and diodes D702 and D703 for controlling the exchange of charge between scan electrodes 606-1˜606-n and sustain electrodes 605-1˜605-n; coil L701; clamp diodes D705 and D707 for suppressing the pressure of the component withstand voltage margin by absorbing spike voltage caused by the counter-electromotive force in coil L701; clamp diodes D704 and D706 for absorbing spike voltage caused by the counter-electromotive force in parasitic inductance; transistor Q701 for applying a voltage VSW (>power-supply voltage VS) that is added to power-supply voltage VS during the write interval in order to facilitate generation of the sustaining discharge; and diode D701 for preventing the flow of a short circuit current between voltage VSW and power-supply voltage VS by way of transistor Q702 due to voltage VSW in cases in which voltage VSW is applied. In this case, point A is the connection point transistors Q706 and Q707; point B is the connection point between the cathode of diode D701 and transistor Q703; and point C is the connection point between the anode of diode D704 and the cathode of diode D706. Panel capacitance C701 is arranged between point A and point B. Scan electrode Y1 is arranged on the point A side of panel capacitance C701, and sustain electrode X1 is arranged on the point B side of panel capacitance C701. X1 and Y1 correspond to X and Y, respectively, shown in FIG. 1.
Next, regarding the operation during the sustaining discharge interval, in the write discharge interval, voltage is applied between scan electrodes 606-1˜606-n and data electrodes 607-1˜607-N based on the display content, whereby charge moves and discharge is generated between the scan electrodes and data electrodes of a portion based on the display content.
Next, panel capacitance C701 is charged when transistors Q702 and Q707 turn ON.
Turning transistors Q702 and Q707 OFF and then turning transistor Q7040N causes panel capacitance C701 and coil L701 to form a resonance circuit, and the charge that has accumulated in panel capacitance C701 flows out as a resonance current and recharges panel capacitance C701 to reverse polarity by way of coil L701.
In FIG. 2, parasitic inductance cannot be ignored if the wiring length between points A and C is lengthened.
Turning now to FIG. 3, an explanation is presented regarding the charge recovery method in sustaining driver circuit that is configured according to the above description.
As the initial state, transistors Q703 and Q706 are each in an ON state, whereby the scan electrode side (point A) is at the potential of power-supply voltage VS and the sustain electrode side (point B) is at the ground potential.
From this state, transistors Q703 and Q706 are set to the OFF state, following which transistor Q705 is placed in the ON state.
A current thereupon flows from the scan electrode side to the sustain electrode side by way of transistor Q705, diode D702, and coil L701, whereby the potential level on the scan electrode side drops and the potential level on the sustain electrode side rises. Here, the slope of the curve of this fall and rise in the potential levels is determined by the resonance period of the product of the inductance of coil L701 and parasitic inductance of the wiring and panel capacitance C701.
After the potential level on the scan electrode side has fallen a certain amount and the potential level on the sustain electrode side rises a certain amount, transistors Q702 and Q707 are placed in the ON state, whereby the potential level of the scan electrode side is clamped to the ground potential and the potential level of the sustain electrode side is clamped to the potential of power-supply voltage VS.
Transistors Q702 and Q707 are next placed in the OFF state, following which transistor Q704 is placed in the ON state.
A current then flows from the sustain electrode side to the scan electrode side by way of coil L701, diode D703 and transistor Q704, whereby the potential level of the sustain electrode side falls and the potential level of the scan electrode side rises.
After the potential level of the sustain electrode side has fallen a certain amount and the potential level of the scan electrode side has risen a certain amount, transistors Q703 and Q706 are placed in the ON state, whereby the potential level of the sustain electrode side is clamped to the ground potential, and the potential level of the scan electrode side is clamped to the potential of power-supply voltage VS.
Self recovery of charge is realized by thus controlling transistors Q702˜Q707 such that the potential on the scan electrode side and the potential on the sustain electrode side shift and charge is exchanged between the scan electrodes and sustain electrodes.
Sustaining driver circuit 601, which is disclosed in Japanese Patent Laid-open No. 344952/1999 and shown in FIG. 4, is made up by: transistor Q901 for clamping sustain electrodes 605-1˜605-n to the potential of power-supply voltage VS; transistor Q902 for clamping sustain electrodes 605-1˜605-n to the ground potential; transistor Q903 for clamping scan electrodes 606-1˜606-n to the potential of power-supply voltage VS; transistor Q904 for clamping scan electrodes 606-1˜606-n to the ground potential; transistors Q905 and Q906 and coil L901 that are connected together in a series between sustain electrodes 605-1˜605-n and scan electrodes 606-1˜606-n; diode D901 that is provided in parallel with transistor Q905; and diode D902 that is provided in parallel with transistor Q906. One end of each of transistors Q905 and Q906 is connected to the two ends of panel capacitance Cp. Coil L901 is arranged between transistors Q905 and Q906.
Next, regarding the operation of the prior-art sustaining driver circuit that is shown in FIG. 4, in the initial state, all transistors Q901˜Q906 are in the OFF state.
From this state, transistors Q901 and Q904 turn ON, whereupon panel capacitance Cp is charged.
Transistors Q901 and Q904 next turn OFF, following which transistor Q905 turns ON, whereupon panel capacitance Cp and coil L901 form a resonance circuit, the charge that has accumulated in panel capacitance Cp flows out as a resonance current, and panel capacitance Cp is recharged to reverse polarity by way of coil L901.
In this example of the prior art, the time during which transistors Q905 and Q906 are ON is adjusted to equal the resonance period of the product of panel capacitance Cp and coil L901.
In recent years, an increase in the sustaining discharge frequency is demanded as a means of improving the luminance of plasma display panels. In order to raise the sustaining discharge frequency, the period of the ON/OFF switching of the transistors is shortened in the sustaining driver circuit such as described hereinabove, whereby the period of shifting of the potential on the sustain electrode side and the potential on the scan electrode side must be shortened.
Raising the sustaining discharge frequency in a case in which the potential in the sustain electrodes and scan electrodes for sustaining discharge is controlled by a single sustaining driver circuit as described hereinabove increases the load on the sustaining driver circuit and gives rise to the problem of concentrated element heat generation. In the sustaining driver circuit shown in FIG. 4 in particular, whether the potential on the sustain electrode side is decreased and this potential is used to raise the potential of the scan electrode side, or the potential of the scan electrode side is decreased and this potential is used to raise the potential of the sustain electrode side, current flows to coil L901 and the generation of heat in coil L901 is considerable.
In the publication of Japanese Patent Laid-open No. 344952/1999, although it is disclosed that the damping resistor that is arranged in parallel with coil L901 can be eliminated if the timing of transistors Q905 and Q906 shown in FIG. 4 is regulated to equal the resonance frequency, in actuality, cases of divergence from the resonance period occur due to variation in the panel capacitance or discrepancies in the circuit elements, and the resulting counter-electromotive force necessitates the introduction of clamp diodes or damping resistance.
In the example shown in FIG. 2, moreover, parasitic inductance exists between points A and C apart from coil L701. The reasons for the existence of this parasitic inductance include:
the arrangement of each clamp switch that is arranged in the vicinity of the panel for reducing the parasitic impedance between clamp switches and electrodes; and
the increase in parasitic inductance that accompanies the increase in wiring length between points A and C with increase in screen size.
Clamp diodes D704 and D706 must be provided to absorb the spike voltage that is caused by counter-electromotive force in this parasitic inductance. In addition, although clamp diodes D705 and D707 are provided to absorb the spike voltage that is caused by the counter-electromotive force in coil L701, in actuality, diode D707 cannot be provided because in cases in which voltage VSW is applied to diode D707, voltage VSW causes a short circuit current to flow between voltage VSW and power-supply voltage VS by way of diode D707. In such a case, spike voltage occurs that is caused by the counter-electromotive force in coil L701. Although it is possible to use a switch in place of diode D707 that turns OFF when VSW is applied, this solution entails higher costs.